From:   Vladimir Oltean <vladimir.oltean@nxp.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Hauke Mehrtens <hauke@hauke-m.de>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>
Subject: Re: [PATCH 5.15 291/917] net: dsa: lantiq_gswip: serialize access to
 the PCE table
Thread-Topic: [PATCH 5.15 291/917] net: dsa: lantiq_gswip: serialize access to
 the PCE table
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Date:   Mon, 15 Nov 2021 23:35:47 +0000
Message-ID: <20211115233547.bduho7ej5ft52cmd@skbuf>
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 <20211115165438.632409127@linuxfoundation.org>
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On Mon, Nov 15, 2021 at 05:56:26PM +0100, Greg Kroah-Hartman wrote:
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
>=20
> [ Upstream commit 49753a75b9a32de4c0393bb8d1e51ea223fda8e4 ]
>=20
> Looking at the code, the GSWIP switch appears to hold bridging service
> structures (VLANs, FDBs, forwarding rules) in PCE table entries.
> Hardware access to the PCE table is non-atomic, and is comprised of
> several register reads and writes.
>=20
> These accesses are currently serialized by the rtnl_lock, but DSA is
> changing its driver API and that lock will no longer be held when
> calling ->port_fdb_add() and ->port_fdb_del().
>=20
> So this driver needs to serialize the access to the PCE table using its
> own locking scheme. This patch adds that.
>=20
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
> Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  drivers/net/dsa/lantiq_gswip.c | 28 +++++++++++++++++++++++-----
>  1 file changed, 23 insertions(+), 5 deletions(-)
>=20
> diff --git a/drivers/net/dsa/lantiq_gswip.c b/drivers/net/dsa/lantiq_gswi=
p.c
> index dbd4486a173ff..1a96df70d1e85 100644
> --- a/drivers/net/dsa/lantiq_gswip.c
> +++ b/drivers/net/dsa/lantiq_gswip.c
> @@ -276,6 +276,7 @@ struct gswip_priv {
>  	int num_gphy_fw;
>  	struct gswip_gphy_fw *gphy_fw;
>  	u32 port_vlan_filter;
> +	struct mutex pce_table_lock;
>  };
> =20
>  struct gswip_pce_table_entry {
> @@ -523,10 +524,14 @@ static int gswip_pce_table_entry_read(struct gswip_=
priv *priv,
>  	u16 addr_mode =3D tbl->key_mode ? GSWIP_PCE_TBL_CTRL_OPMOD_KSRD :
>  					GSWIP_PCE_TBL_CTRL_OPMOD_ADRD;
> =20
> +	mutex_lock(&priv->pce_table_lock);
> +
>  	err =3D gswip_switch_r_timeout(priv, GSWIP_PCE_TBL_CTRL,
>  				     GSWIP_PCE_TBL_CTRL_BAS);
> -	if (err)
> +	if (err) {
> +		mutex_unlock(&priv->pce_table_lock);
>  		return err;
> +	}
> =20
>  	gswip_switch_w(priv, tbl->index, GSWIP_PCE_TBL_ADDR);
>  	gswip_switch_mask(priv, GSWIP_PCE_TBL_CTRL_ADDR_MASK |
> @@ -536,8 +541,10 @@ static int gswip_pce_table_entry_read(struct gswip_p=
riv *priv,
> =20
>  	err =3D gswip_switch_r_timeout(priv, GSWIP_PCE_TBL_CTRL,
>  				     GSWIP_PCE_TBL_CTRL_BAS);
> -	if (err)
> +	if (err) {
> +		mutex_unlock(&priv->pce_table_lock);
>  		return err;
> +	}
> =20
>  	for (i =3D 0; i < ARRAY_SIZE(tbl->key); i++)
>  		tbl->key[i] =3D gswip_switch_r(priv, GSWIP_PCE_TBL_KEY(i));
> @@ -553,6 +560,8 @@ static int gswip_pce_table_entry_read(struct gswip_pr=
iv *priv,
>  	tbl->valid =3D !!(crtl & GSWIP_PCE_TBL_CTRL_VLD);
>  	tbl->gmap =3D (crtl & GSWIP_PCE_TBL_CTRL_GMAP_MASK) >> 7;
> =20
> +	mutex_unlock(&priv->pce_table_lock);
> +
>  	return 0;
>  }
> =20
> @@ -565,10 +574,14 @@ static int gswip_pce_table_entry_write(struct gswip=
_priv *priv,
>  	u16 addr_mode =3D tbl->key_mode ? GSWIP_PCE_TBL_CTRL_OPMOD_KSWR :
>  					GSWIP_PCE_TBL_CTRL_OPMOD_ADWR;
> =20
> +	mutex_lock(&priv->pce_table_lock);
> +
>  	err =3D gswip_switch_r_timeout(priv, GSWIP_PCE_TBL_CTRL,
>  				     GSWIP_PCE_TBL_CTRL_BAS);
> -	if (err)
> +	if (err) {
> +		mutex_unlock(&priv->pce_table_lock);
>  		return err;
> +	}
> =20
>  	gswip_switch_w(priv, tbl->index, GSWIP_PCE_TBL_ADDR);
>  	gswip_switch_mask(priv, GSWIP_PCE_TBL_CTRL_ADDR_MASK |
> @@ -600,8 +613,12 @@ static int gswip_pce_table_entry_write(struct gswip_=
priv *priv,
>  	crtl |=3D GSWIP_PCE_TBL_CTRL_BAS;
>  	gswip_switch_w(priv, crtl, GSWIP_PCE_TBL_CTRL);
> =20
> -	return gswip_switch_r_timeout(priv, GSWIP_PCE_TBL_CTRL,
> -				      GSWIP_PCE_TBL_CTRL_BAS);
> +	err =3D gswip_switch_r_timeout(priv, GSWIP_PCE_TBL_CTRL,
> +				     GSWIP_PCE_TBL_CTRL_BAS);
> +
> +	mutex_unlock(&priv->pce_table_lock);
> +
> +	return err;
>  }
> =20
>  /* Add the LAN port into a bridge with the CPU port by
> @@ -2106,6 +2123,7 @@ static int gswip_probe(struct platform_device *pdev=
)
>  	priv->ds->priv =3D priv;
>  	priv->ds->ops =3D priv->hw_info->ops;
>  	priv->dev =3D dev;
> +	mutex_init(&priv->pce_table_lock);
>  	version =3D gswip_switch_r(priv, GSWIP_VERSION);
> =20
>  	np =3D dev->of_node;
> --=20
> 2.33.0
>=20
>=20
>

As discussed on the v5.14 backport, this patch can be dropped.=